This seems more plausible than Google actually giving a crap about clothed women being objectified on a niche forum.

I seriously doubt they actually look at much content.

It is probably some algorithm that looks at commonality between sites that are on a black list and the sites that are not. If there is enough matches a form letter is sent.

The rule is unclear.

Pornography, adult or mature content

The Supreme Court last year didn't draw a clear line about what is allowed on broadcast TV.

Quote:

The decision states, “The Commission failed to give Fox or ABC fair notice prior to the broadcasts in question that fleeting expletives and momentary nudity could be found actionably indecent, the Commission’s standards as applied to these broadcasts were vague.”

What does mature mean?

Perfect Dark was a M game. It was a futuristic world shooting game that was cartoonish at times.

Grand Theft Auto is a M game.
A few other games have all the violence and also show some boob.

This is like Nintendo back in the day censoring this without getting their actually fingerprints on it. If you didn't fall in line you were gonna have a problem getting a game on the market.

There are numerous music videos on youtube that have mature content how are they OK for ads?

It seems like they should have this figured out. The 18+ or 21+ stuff is not for them.
There is also probably a segment that is Hallmark/Barney kind of content that should have ads that stay that way.

The VAST majority of the market is in the middle and how they are implementing the policy against the little guys is unfairly keeping them under their thumb.

Google doesn't have a problem with most types of adult content showing up in their search results. They have a problem with their adsense advertisements showing up on sites with adult content. This is to keep their advertisers happy (and keep in mind that Google is essentially an advertising company).